1. Field of the Invention
The present invention relates to a separator unit and a fuel cell having a separator unit, and more particularly to a separator unit which is light in weight and small in size and is capable of guiding a coolant such as cooling water to flow along its surface, and a fuel cell having such a separator unit.
2. Description of the Related Art
FIG. 12 of the accompanying drawings shows in exploded perspective a pair of unit cells 2 of a typical fuel cell 1. As shown in FIG. 12, the fuel cell 1 has a stacked assembly 3 comprising a plurality of unit cells 2 electrically connected in series with each other and stacked in the direction indicated by an arrow A in FIG. 12.
Each of the unit cells 2 comprises an electrolyte electrode assembly 7 made up of an anode electrode 4, a cathode electrode 5, and an electrolyte layer 6 interposed between the anode electrode 4 and the cathode electrode 5, and first and second separators 9, 10 of metal sandwiching a gasket 8 which accommodates and holds the electrolyte electrode assembly 7.
Each of the anode electrode 4 and the cathode electrode 5 has a gas diffusion layer (not shown) made of carbon cloth or the like and an electrode catalyst layer (not shown) made of porous carbon particles carrying a platinum alloy on their surfaces and deposited uniformly on the surface of the gas diffusion layer. The anode electrode 4 and the cathode electrode 5 are electrolyte electrode to the electrolyte layer 6 with their electrode catalyst layers facing each other across the electrolyte layer 6. The electrolyte layer 6 comprises a solid polymer ion exchange membrane in the form of a thin membrane of perfluorosulfonic acid impregnated with water.
Each of the first separator 9, the second separator 10, and the gasket 8 has a first gas inlet passage 11 defined in an upper left corner thereof for passing a fuel gas therethrough and a first gas outlet passage 12 defined in a lower right corner thereof, diagonally opposite to the upper left corner, for passing a fuel gas that has been used therethrough. Similarly, each of the first separator 9, the second separator 10, and the gasket 8 has a second gas inlet passage 13 defined in an upper right corner thereof for passing an oxygen-containing gas therethrough and a second gas outlet passage 14 defined in a lower left corner thereof, diagonally opposite to the upper right corner, for passing therethrough an oxygen-containing gas that has been used and water (water vapor) generated by an electric power generating reaction in the fuel cell 1.
The first separator 9 has a plurality of first hollow ridges 15 on a surface thereof which faces the anode electrode 4, for supplying and discharging the fuel gas (e.g., a hydrogen-containing gas mainly composed of hydrogen) to and from the anode electrode 4. The second separator 10 has a plurality of second hollow ridges 16 on a surface thereof which faces the cathode electrode 5, for supplying and discharging the oxygen-containing gas (e.g., air) to and from the cathode electrode 5. A branch groove 17 and a collection groove 18 are defined between the first hollow ridges 15, the first gas inlet passage 11, and the first gas outlet passage 12. Similarly, a branch groove 19 and a collection groove 20 are defined between the second hollow ridges 16, the second gas inlet passage 13, and the second gas outlet passage 14.
FIG. 13 of the accompanying drawings shows in enlarged fragmentary cross section two unit cells 2 that are stacked together. As shown in FIG. 13, the first hollow ridges 15 and the second hollow ridges 16 are successively arranged with first troughs 21 and second troughs 22, respectively, interposed therebetween. In the stacked assembly 3, the first hollow ridges 15 of the first separator 9 of the upper unit cell 2 in FIG. 12 and the second hollow ridges 16 of the second separator 10 of the lower unit cell 2 have respective crest surfaces held in abutment against each other.
As shown in FIG. 12, each of the first separator 9, the second separator 10, and the gasket 8 has a cooling water inlet passage 23 defined in a lower edge thereof and extending in the direction indicated by an arrow B from the second gas outlet passage 14 to the first gas outlet passage 12. Each of the first separator 9, the second separator 10, and the gasket 8 also has a cooling water outlet passage 24 defined in an upper edge thereof and extending in the direction indicated by the arrow B from the first gas inlet passage 11 to the first gas inlet passage 13.
For operating the fuel cell 1 thus constructed, the fuel gas and the oxygen-containing gas are supplied to the fuel cell 1 respectively through the first gas inlet passage 11 and the first gas inlet passage 13. These supplied gases are distributed by the branch grooves 17, 19 into the first hollow ridges 15 and the second hollow ridges 16 and supplied for reaction over the electrode catalyst layers of the anode electrode 4 and the cathode electrode 5. Unreacted gases are collected by the collection grooves 18, 19, and discharged through the first gas outlet passage 12 and the second gas outlet passage 14.
When the fuel cell 1 is in operation, a coolant, typically cooling water, is also introduced into the cooling water inlet passages 23. The introduced cooling water flows in the stacking direction of the stacked assembly 3, and is then discharged out of the fuel cell 1 through the cooling water outlet passages 24.
For efficiently cooling the unit cells 2, it is preferable to pass the cooling water in the direction indicated by an arrow C in FIG. 12 perpendicular to the stacking direction of the stacked assembly 3, as well as in the stacking direction (indicated by the arrow A) of the stacked assembly 3. One approach would be to pass the cooling water in the plane of the first separator 9 and the second separator 10 from the cooling water inlet passages 23 to the cooling water outlet passages 24.
However, since the first hollow ridges 15 of the first separator 9 of the upper unit cell 2 in FIG. 12 and the second hollow ridges 16 of the second separator 10 of the lower unit cell 2 have their crest surfaces held in abutment against each other, the abutting crest surfaces would present an obstacle to the flow of the cooling water. Therefore, the cooling water cannot be passed in the direction indicated by the arrow C in FIG. 12.
One solution is to place a bar-shaped spacer 25 between the first separator 9 and the second separator 10, as shown in FIG. 14 of the accompanying drawings, spacing the crest surfaces of the first hollow ridges 15 and the second hollow ridges 16 from each other. This proposal, however, is disadvantageous in that the fuel cell 1 is constructed of an increased number of components and has its weight and volume increased by the added spacers 25.
According to another solution shown in FIGS. 15 and 16 of the accompanying drawings, the cooling water inlet passage 23 to the cooling water outlet passage 24 are lined up with the first gas inlet passage 11 and the second gas outlet passage 14, and the first gas outlet passage 12 and the second gas inlet passage 13, for passing the cooling water longitudinally or diagonally in the stacked assembly 3. However, since the structures shown in FIGS. 15 and 16 fail to distribute the cooling water well in the stacked assembly 3, air bubbles introduced into the cooling water cannot be eliminated, resulting in a reduction in the cooling efficiency. Furthermore, the passages 11, 12, 13, 14, 23, 24 are reduced in size, making it difficult to pass the fuel gas and the oxygen-containing gas at a high rate, with the result that the fuel cell 1 has its power generating efficiency lowered. In addition, it is difficult to change the positions of the passages 11, 12, 13, 14, 23, 24. Stated otherwise, the layout of the passages 11, 12, 13, 14, 23, 24 suffers limited freedom.